Insights into the Inhibition Mechanism of Human Pancreatic α-Amylase, a Type 2 Diabetes Target, by Dehydrodieugenol B Isolated from Ocimum tenuiflorum.

Use of human pancreatic α-amylase (HPA) inhibitors is one of the effective antidiabetic strategies to lower postprandial hyperglycemia via reduction in the dietary starch hydrolysis rate. Many natural products from plants are being studied for their HPA inhibitory activity. The present study describes isolation of dehydrodieugenol B (DDEB) from Ocimum tenuiflorum leaves using sequential solvent extraction, structure determination by one-dimensional (1D) and two-dimensional (2D) NMR analyses, and characterization as an HPA inhibitor using kinetics, binding thermodynamics, and molecular docking. DDEB uncompetitively inhibited HPA with an IC50 value of 29.6 µM for starch and apparent K i ' of 2.49 and Ki of 47.6 µM for starch and maltopentaose as substrates, respectively. The circular dichroism (CD) study indicated structural changes in HPA on inhibitor binding. Isothermal titration calorimetry (ITC) revealed thermodynamically favorable binding (ΔG of -7.79 kcal mol-1) with a dissociation constant (K d) of 1.97 µM and calculated association constant (K a) of 0.507 µM. Molecular docking showed stable HPA-inhibitor binding involving H-bonds and Pi-alkyl, alkyl-alkyl, and van der Waals (vDW) interactions. The computational docking results support the noncompetitive nature of DDEB binding. The present study could be helpful for exploration of the molecule as a potential antidiabetic drug candidate to control postprandial hyperglycemia.

α-Geminal disubstituted pyrrolidine iminosugars and their C-4-fluoro analogues: Synthesis, glycosidase inhibition and molecular docking studies.

A simple strategy for the synthesis of α-geminal disubstituted pyrrolidine iminosugars 3a-c and their C-4 fluorinated derivatives 4a-c has been described from d-glucose. The methodology involves the Corey-Link and Jocic-Reeve reaction with 3-oxo-α-d-glucofuranose and nucleophilic displacement reaction to get the furanose fused pyrrolidine ring skeleton with requisite CH2OH/CO2H functionalities at C-3. The fluorine substituent in target molecules was introduced by nucleophilic displacement of -OTf in 9a/9c with CsF. Appropriate manipulation of the anomeric carbon in the furanose fused pyrrolidine ring skeleton afforded α-geminal disubstituted pyrrolidine iminosugars 3a-c and C-4 fluoro derivatives 4a-c. The pyrrolidine iminosugars 3a and 3c were found to be potent inhibitors of α-galactosidase while, the fluoro derivatives 4a and 4b showed strong inhibition of ß-glucosidase and ß-galactosidase, respectively. These results were substantiated by in silico molecular docking studies.

Iminosugars Spiro-Linked with Morpholine-Fused 1,2,3-Triazole: Synthesis, Conformational Analysis, Glycosidase Inhibitory Activity, Antifungal Assay, and Docking Studies.

Synthesis of iminosugars 1, 2, 3a, and 4a and N-alkyl (ethyl, butyl, hexyl, octyl, decyl, and dodecyl) derivatives 3b-g and 4b-g spiro-linked with morpholine-fused 1,2,3-triazole is described. Conformation of the piperidine ring in each spiro-iminosugar was evaluated by 1H NMR spectroscopy, and conformational change in N-alkylated compounds 4b-g with respect to parent spiro-iminosugar 4a is supported by density functional theory calculations. Out of 16 new spiro-iminosugars, the spiro-iminosugars 3a (IC50 = 0.075 µM) and 4a (IC50 = 0.036 µM) were found to be more potent inhibitors of α-glucosidase than the marketed drug miglitol (IC50 = 0.100 µM). In addition, 3a (minimum inhibition concentration (MIC) = 0.85 µM) and 4a (MIC = 0.025 µM) showed more potent antifungal activity against Candida albicans than antifungal drug amphotericin b (MIC = 1.25 µM). In few cases, the N-alkyl derivatives showed increase of α-glucosidase inhibition and enhancement of antifungal activity compare to the respective parent iminosugar. The biological activities were further substantiated by molecular docking studies.

Azetidine- and N-carboxylic azetidine-iminosugars as amyloglucosidase inhibitors: synthesis, glycosidase inhibitory activity and molecular docking studies.

A simple strategy for the synthesis of hitherto unknown azetidine iminosugars 2a­2c and N-carboxylic azetidine iminosugar 2d has been reported. The methodology involves the conversion of 1,2:5,6-di-O-isopropylidene-3-oxo-α-D-glucofuranose 3 to 3-azido-3-deoxy-3-C-(formyl)-1,2:5,6-di-O-isopropylidene-α-D-glucofuranose 5 using the Jocic­Reeve and Corey­Link approaches. Compound 5 was transformed to 5-OTs 10/5-OMs 19 derivatives that on intramolecular nucleophilic displacement with in situ generated 3-amino functionality afforded the key azetidine ring skeletons 11 and 20, respectively. Hydrolysis of the 1,2-acetonide group and manipulation of the anomeric carbon in 12 provided azetidine iminosugars 2a­2c. In an attempt to synthesize azetidine iminosugars with an additional 4-hydroxymethyl group from 20, we encountered an interesting observation wherein the N-Cbz group in 20 hydrolyzed to the N-COOH functionality under TFA:H2O conditions that gave access for the synthesis of N-carboxylic azetidine iminosugar 2d. The glycosidase inhibitory activity of 2a­2d and intermediates 2e­f was studied with various glycosidases and was compared with Miglitol and 1-deoxynojirimycin (DNJ). Azetidine iminosugars 2 were found to inhibit amyloglucosidase with competitive type inhibition, amongst which 2d was found to be more active than Miglitol and DNJ. These results were substantiated by in silico molecular docking studies.